A. Field of the Invention
The present invention is directed to a method for packaging hot-melt pressure sensitive adhesive compositions. In particular, the present method is directed to a method for the high throughput tack-free packaging of a thermoplastic or thermosetting hot-melt pressure sensitive adhesive composition, wherein the packaging is both tack-free and compatible with the adhesive composition in the molten state. The present invention is useful because it provides a clean and convenient method to handle the otherwise tacky hot-melt adhesive composition and eliminates the waste typically associated with its packaging.
B. Background
Hot-melt, pressure sensitive adhesive compositions are typically applied while in the molten or liquid state. However, at room temperature, they are generally solids and they are sold to the industry in the form of blocks. However, the solid block are so tacky that if untreated, they would stick to hands, each other, dirt and anything else that they contacted. Accordingly, various methods have been developed to provide for the low-tack or tack-free handling of hot-melt adhesive compositions.
A variety of methods employ a tack-less micronized powder that is dusted on the outer surface of the hot-melt, pressure sensitive adhesive as it cools. Moreover, they need to be applied at the appropriate temperature. A problem with these micronized powders is that they are expensive to make and thus, costly to use.
U.S. Pat. No. 4,748,796, which issued Oct. 22, 1988, and U.S. Pat. No. 4,755,245, which issued Jul. 5, 1988, disclose a method for powder coating a hot-melt, pressure sensitive adhesive composition by electrostatically coating a mold or cavity with a powder, pouring the hot-melt adhesive into the powder coated mold, and then dusting the top of the hot-melt in the mold cavity.
U.S. Pat. No. 5,333,439 discloses coating a micronized powder for the release packaging of a hot-melt pressure sensitive adhesive composition in a siliconized plastic film.
Other methods pour the hot-melt, pressure sensitive adhesive into molds that are sprayed with a film of non self-sticking hot-melt material. Still other methods squeeze the molten hot-melt, pressure sensitive adhesive as an inner layer surrounded by a molten outer layer of a compatible non-tacky polymer. Such methods are expensive because they require separate vats of molten materials. The latter method is particularly expensive to operate because it requires a specialized piece of equipment with precisely controlled flows to completely envelop the hot-melt in molten non-tack polymer.
U.S. Pat. Nos. 5,373,682 and 5,392,592 disclose a method for the vertical packaging a hot-melt, pressure sensitive adhesive by extruding the molten hot-melt down into a continuous cylindrical tube of plastic film that is liquid cooled on the outside to keep the molten hot-melt from melting through. The plastic film is selected to be meltable with the adhesive composition and blendable therein. To form appropriate sized cartridges or tubes of adhesive, the plastic film containing the molten adhesive is squeezed with voider rolls, which crimp the packaging while cooling the molten adhesive at the crimped end. The '592 patent discloses crimping the ends and holding them closed with a meltable plastic wire. The resulting product resembles a series of sausage links hanging end to end. A problem with these methods is that the output of each machine is relatively slow, since each machine has a single nozzle that is only capable of extruding a single cartridge or tube of adhesive at a time. Moreover, the output is limited by the time it takes each chilled voided roll to crimp and cool the ends of each segment of adhesive before release.
U.S. Pat. No. 5,387,623 discloses a method for the waste-free packaging of hot-melt adhesive composition in a biodegradable polymeric packaging material. In the '623 patent, the biodegradable packaging is meltable in the adhesive without adhesive effect. The method of the '623 patent is very slow because it requires providing an individual portion of the hot-melt adhesive composition and solidifying the individual portion before packaging it.
Accordingly, an object of the present invention is to provide a method for the high throughput packaging of a hot-melt adhesive composition in a tack-free manner, wherein the packaging is meltable therein without adverse effect.